From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752792AbcDKKbJ (ORCPT ); Mon, 11 Apr 2016 06:31:09 -0400 Received: from foss.arm.com ([217.140.101.70]:48371 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751216AbcDKKbI (ORCPT ); Mon, 11 Apr 2016 06:31:08 -0400 Subject: Re: [PATCH] scatterlist: use sg_dma_len() in sg_set_page() To: Shawn Guo , Catalin Marinas , Will Deacon References: <1460342864-27891-1-git-send-email-shawnguo@kernel.org> Cc: linux-arm-kernel@lists.infradead.org, Andrew Morton , linux-kernel@vger.kernel.org, Arnd Bergmann From: Robin Murphy Message-ID: <570B7CE8.3020307@arm.com> Date: Mon, 11 Apr 2016 11:31:04 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:38.0) Gecko/20100101 Thunderbird/38.6.0 MIME-Version: 1.0 In-Reply-To: <1460342864-27891-1-git-send-email-shawnguo@kernel.org> Content-Type: text/plain; charset=windows-1252; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi Shawn, On 11/04/16 03:47, Shawn Guo wrote: > The macro sg_dma_len(sg) is commonly used to retrieve length of sg, > which could be 'dma_length' or 'length' field, depending on whether > NEED_SG_DMA_LENGTH is enabled or not. On the other hand, many driver > code use helper function sg_set_page() to set an sg entry pointing at > a page, with offset and length set up in one call. But sg_set_page() > does not consider NEED_SG_DMA_LENGTH case and only set up 'length' > field. This causes problem on platforms like ARM64, where > NEED_SG_DMA_LENGTH is enabled by default, i.e. sg_set_page() sets up > 'length' while sg_dma_len(sg) returns 'dma_length' field. > > The patch changes sg_set_page() to use sg_dma_len() for sg length setup > as well, so that NEED_SG_DMA_LENGTH case can be handled. > > Signed-off-by: Shawn Guo > --- > include/linux/scatterlist.h | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/include/linux/scatterlist.h b/include/linux/scatterlist.h > index 556ec1ea2574..b0e32ea594c3 100644 > --- a/include/linux/scatterlist.h > +++ b/include/linux/scatterlist.h > @@ -114,7 +114,7 @@ static inline void sg_set_page(struct scatterlist *sg, struct page *page, > { > sg_assign_page(sg, page); > sg->offset = offset; > - sg->length = len; > + sg_dma_len(sg) = len; This looks wrong. If a driver is building a scatterlist, then it needs to fill in the page, offset and length fields to describe the physical layout - leaving sg->length uninitialised would be a recipe for disaster - then pass it to the DMA API. Only the DMA API implementation should be setting dma_addr and dma_len, and they may not correspond to the physical layout at all (e.g. an IOMMU could concatenate the entire list into a single much longer segment at whatever arbitrary DMA address it chooses). Is there some particular driver hiccup behind this? Robin. > } > > static inline struct page *sg_page(struct scatterlist *sg) >